Fiesta failed on emisions

Hi to all
I am repairing a Fiesta 1117cc 1993 with CFI for a MOT retest one of the failure items is emisions like
fails CO test 0.79
passes HC at 178 Lambda pass at 1.03
so to sum up just fails on the CO should be up to 0.30 max I guess the cat has failed do you agree as this car belongs to a student and I am trying to keep costs down. The engine has had a full service in the last 6 x months
thanks in advance mike
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It sounds most like the car was not fully stinking hot, I have several of these that have the same symptoms but they pass if they are really hot.
mrcheerful
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mrcheerful

If it's got a cat and is newer than a certain date, don't the MOT people measure the oil temp before taking readings?
--
*You never really learn to swear until you learn to drive *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Ticker was seen penning the following ode to ... whatever:

You may well have guessed wrong, it could be the lambda sensor as well (and that's somewhat cheaper to replace...). I'd get it hooked up to some proper diagnostic equipment first as that may well point you in the right direction.

Which probably makes bog-all difference if one of the engine management sensors has gone south.
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Timo Geusch
'92 Nissan Skyline GTS-T
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and
my favorite on those is fuel pressure -- George
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Check the throttle position sensor first, these can cause over fuelling, and are *extremely* common.
You also need to check the vacuum pipe to the MAP sensor (on the bulkhead), these get filled with fuel and eventually perish and collapse. If so, then you need to replace it, and also fit the one way valve too.
Check that the breathers are clear too, these commonly gunge up.
What kind of 'full' service? If it was a Kwik-Fit type place then suspect that a full service wasn't carried out completely.
Check also valve clearances and plug gaps.
Than, as already said, get it stinking hot before you take it back for the retest.
--
Andy Hewitt ** FAF#1, (Ex-OSOS#5) - FJ1200 ABS
Honda Civic 16v: Windows free zone (Mac G5 Dual Processor)
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and
Fiesta CFi's can be sods, make sure the motor is fully hot before the test and that the thermostat is allowing it to be- the gauge should be reading in the middle of the NORMAL section. Any less- change the 'stat and give it a hard fast run at motorway speed just prior to the test so its really hot.
If it still fails then favorites on the CFI are faulty Air temp and water temp sensors- check the ATS first- they tend to get melted if the engine's ever spat back through the inlet manifold- quite common!
Tim..
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wrote:

Assuming that the engine was hot and assuming there are no air leaks at all (inlet or exhaust) then a lambda figure of 1.03 says that the mixture is on the weak side and there should be Ox present in the exhaust to "feed" the cat. Generally a failed temp sensor, lambda sensor etc would create a rich mixture and the lambda reading would be below 1.0 i.e. 0.92
A CO of 0.79 is not mega high, so from those figures I would be suspecting a very weak or failed cat.
Regards, Graham L http://www.lambdasensor.com http://www.injectorcleaning.co.uk
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